Microphone assemblies with through-silicon vias

Title: Microphone assemblies with through-silicon vias.Abstract: Microphone assemblies may be provided that have microelectromechanical systems microphones and associated application-specific integrated circuits mounted to printed circuit boards. The application-specific integrated circuits may contain amplifier circuitry for amplifying microphone signals from the microphone. One or more though-silicon vias may be formed in the application-specific integrated circuit that serve as an acoustic port through which sound may pass. The application-specific integrated circuit may be embedded in the printed circuit board and the microphone may be mounted to the upper surface of the printed circuit board, the application-specific integrated circuit and microphone may be stacked on the upper surface of the printed circuit board, or the microphone and application-specific integrated circuit may be mounted to the printed circuit board so that the microphone is received within an opening in the printed circuit board. ...

BACKGROUND

This relates to assemblies of electrical and mechanical components for electronic devices, and, more particularly, to assemblies including acoustic components such as microphones.

Electronic devices often include acoustic components. For example, speakers may be used to produce sound for a user. Microphones may be used to gather audio input signals. In devices such as noise cancelling headphones, microphones may be used to gather ambient noise signals. Microphones may also be used to collect a user's voice or other sound input. For example, microphones may be used in cellular telephone headsets to gather a user's voice during a telephone call.

Space-constrained accessories such as headsets and other electronic equipment may benefit from compact microphones. It can be challenging, however, to reduce the size of conventional microphones. If care is not taken, acoustic quality will be degraded or microphone assemblies will not be sufficiently compact.

It would therefore be desirable to be able to provide improved microphone assemblies.

One or more though-silicon vias may be formed in the application-specific integrated circuit that serve as an acoustic port through which sound may pass. The application-specific integrated circuit may be thinned prior to through-silicon via formation. In the microphone assembly, the a microphone may be aligned with respect to the application-specific integrated circuit so that sound passes through the acoustic port and reaches the microphone diaphragm through the microphone opening.

With one illustrative arrangement, the application-specific integrated circuit may be embedded in the printed circuit board and the microphone may be mounted to the upper surface of the printed circuit board. With another illustrative arrangement, the application-specific integrated circuit and microphone may be stacked on the upper surface of the printed circuit board. With another illustrative arrangement, the microphone and application- specific integrated circuit may be mounted to the printed circuit board so that the microphone is received within an opening in the printed circuit board.

Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of an illustrative microphone assembly with an application- specific integrated circuit that has through-silicon vias that serve as an acoustic port and that has been embedded in a printed circuit board under a microelectromechanical systems microphone in accordance with the embodiment of the present invention.

FIG. 2 is a cross-sectional side view of a portion of the illustrative microphone assembly of FIG. 2 in the vicinity of a via in accordance with an embodiment of the present invention.

FIG. 3 is a cross-sectional side view of an illustrative microphone assembly that includes an application-specific integrated circuit with through-silicon vias that serve as an acoustic port mounted on the surface of a printed circuit board under a microelectromechanical systems microphone in accordance with an embodiment of the present invention.

FIG. 4 is a cross-sectional side view of an illustrative microphone assembly in which a microelectromechanical systems microphone has been mounted in an opening in a printed circuit board and in which an application-specific integrated circuit with through-silicon vias that serve as an acoustic port has been mounted under the microelectromechanical systems microphone in accordance with an embodiment of the present invention.

FIG. 5 is a top view of a microphone assembly of the type shown in FIG. 4 in accordance with an embodiment of the present invention.

FIG. 6 is an exploded cross-sectional side view of a microphone assembly of the type shown in FIGS. 4 and 5 showing how the microphone assembly may be assembled in accordance with an embodiment of the present invention.

FIG. 7 is a top view of an illustrative microphone assembly in which a microelectromechanical systems microphone has been mounted in a corner opening in a printed circuit board in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

This relates to assemblies that include acoustic components such as microphones and speakers. Illustrative arrangements in which the assemblies are formed from microphones are sometimes described herein as examples, but arrangements that use speakers, combinations of speakers and microphones, or other configurations may be used if desired.

An illustrative microphone assembly is shown in FIG. 1. As shown in FIG. 1, microphone assembly 10 may be formed by mounting a microphone such as microphone 12 and an associated application-specific integrated circuit such as integrated circuit 32 to a common substrate such as printed circuit board 24. One or more openings in application- specific integrated circuit 32 such as one or more through- silicon vias 34 may serve as an acoustic port for assembly 10. With this arrangement, sound from the surrounding environment may enter microphone opening 14 in microphone 12 through the acoustic port formed from vias 34.

Microphone 12 may be a microelectromechanical systems (MEMs) microphone formed from a silicon substrate or may be a microphone that is implemented using other suitable microphone technologies. As shown in FIG. 1, microphone 12 may have a diaphragm such as diaphragm 16. Diaphragm 16 may be located within microphone opening 14 in the lower surface of microphone 12. An acoustic cavity for microphone 12 may be formed within the same silicon substrate as diaphragm 16 (see, e.g., cavity 18). Arrangements in which cavity 18 is formed within the silicon substrate from which the microphone diaphragm is formed are sometimes referred to as “back volume in die” arrangements. In configurations of the type shown in FIG. 1 in which microphone 12 is mounted efficiently in assembly 10, there may be an increased amount of space available in microphone 12 for forming cavity 18. Increasing the space used for back volume cavity space 18 may help improve microphone performance (e.g., signal-to- noise ratio). Other acoustic cavity configurations may be used for microphone 12 if desired. The use of back volume in die MEMs microphones is merely illustrative.

For satisfactory operation, it is generally desirable for application-specific integrated circuit 32 to be mounted in the vicinity of microphone 12. In the illustrative configuration of FIG. 1, application-specific integrated circuit 32 is embedded within printed circuit board 24 under MEMs microphone 12 (e.g., by forming a cavity within one or more of the dielectric layers that make up printed circuit board 24 and by mounting circuit 32 in the cavity during the process of forming printed circuit board 24). Printed circuit board 24 may be a rigid printed circuit board (e.g., a fiberglass-filled epoxy printed circuit board such as an FR-4 printed circuit board) or a flexible printed circuit board.

One or more through-silicon vias 34 (i.e., openings that pass through the silicon die used to form application-specific integrated circuit 32) may be used to form an acoustic port (i.e., a passageway that allows sound to pass through integrated circuit 32). Vias 34 may be formed by etching (e.g., dry and/or wet etching). To facilitate via formation, application-specific integrated circuit 32 may be thinned before vias 34 are etched. For example, application-specific integrated circuit 32 may be thinned to a thickness of about 50-300 microns (e.g., 100-200 microns) by polishing (e.g., using chemical-mechanical polishing operations).

Opening 36 in printed circuit board 24 may pass through printed circuit board from lower surface 38 to upper surface 40 and may be aligned with the acoustic port in integrated circuit 32 formed from through-silicon vias 34. This allows sound to pass through opening 36 and the acoustic port in application-specific integrated circuit 32 to reach microphone opening 14 of microphone 12 and diaphragm 16.

Diaphragm 16 and the audio circuitry on application-specific integrated circuit 32 may be interconnected using solder, conductive traces, and other suitable interconnect paths. As shown in FIG. 1, for example, solder balls 26 may be used to mount microphone 12 to upper surface 40 of printed circuit board 24. Vias such as via 28 (e.g., laser vias or other suitable vias) may be formed in printed circuit board 24 to connect solder bumps 26 to circuitry on application-specific integrated circuit (shown by the interconnect of via 28 and trace 30 on application-specific integrated circuit 32 in the FIG. 1 example).

If desired, an encapsulant layer such as layer 20 (e.g., an epoxy layer or other suitable material) may be used to form an environmental seal for microphone 12. Shield 22 may help to reduce electrical interference and may help protect microphone 12 from environmental exposure.

FIG. 2 is a cross-sectional side view of via 28 of FIG. 1. As shown in FIG. 2, via 28 may have metal 44 that is formed within via opening 42. Metal 44 may interconnect solder ball 26 to trace 30 on application-specific integrated circuit 32. Microphone 12 may have traces such as pad 43. Pad 43 may be electrically coupled to diaphragm 16 (FIG. 1). When mounting microphone 12, solder ball 26 may interconnect pad 43 to via metal 44 in via 28. Printed circuit 24 may contain traces that interconnect microphone 12 and application specific integrated circuit to wires and other circuitry in an electrical device.

If desired, microphone 12 and application-specific integrated circuit 32 may be mounted on upper surface 40 of printed circuit board 24. As shown in FIG. 3, for example, application-specific integrated circuit 32 may be a double-sided integrated circuit that has solder pads on both its upper and lower surfaces. Active circuitry may be formed on one of the two surfaces of application-specific integrated circuit 32 (e.g., the upper surface). Through-silicon vias such as vias 49 that are filled with metal may be used in forming interconnects that route signals from the upper surface of application-specific integrated circuit 32 to the lower surface of application-specific integrated circuit.

Solder pads on the upper surface of application-specific integrated circuit 32 may be soldered to corresponding solder pads on the lower surface of microphone 12 using solder 46. Solder pads on the lower surface of application-specific integrated circuit 32 may be soldered to corresponding solder pads on upper surface 40 of printed circuit board 24 using solder 48.

Application-specific integrated circuit 32 may have one or more through-silicon vias 34 that form an acoustic port. Opening 36 in printed circuit board 24 may pass through printed circuit board 24 from lower surface 38 to opposing upper surface 40 and may be aligned with the acoustic port. Sound may travel through opening 36, the acoustic port formed from through-silicon vias 34, and opening 14 in microphone 12 to reach diaphragm 16. As shown by dashed acoustic cavity line 18, microphone 12 may have a back volume in die configuration. Microphone 12 and application-specific integrated circuit 32 may be covered with encapsulant 20.

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20121206|20120308045|microphone assemblies with through-silicon vias|Microphone assemblies may be provided that have microelectromechanical systems microphones and associated application-specific integrated circuits mounted to printed circuit boards. The application-specific integrated circuits may contain amplifier circuitry for amplifying microphone signals from the microphone. One or more though-silicon vias may be formed in the application-specific integrated circuit that serve |